Semiconductor device packages or integrated circuit (IC) chip carriers find use in a variety of high-density electronics applications. The integrated circuits or semiconductor devices are typically protected from the external environment by transfer molding a thermoset or thermoplastic resin about the device. This package provides protection from dust, humidity and other environmental factors which can destroy the delicate circuitry.
A major problem associated with these types of packages is that they do not provide shielding from electromagnetic radiation, such as radio frequency interference (RFI) or electromagnetic interference (EMI). This ability to shield high-frequency circuits, especially in electronic equipment such as two-way radios, is critical. Conventional shielding systems are generally characterized by a metallic enclosure constructed to surround the device to be shielded. This enclosure acts either to protect the electrical equipment from external RFI or EMI signals or to prevent the escape of RFI or EMI signals generated by the device. Typically, these shielded enclosures are made from a conductive material that is electrically coupled to an appropriate ground. In the prior art, shielded enclosures have been made by attaching a drawn metallic casing over the transfer molded package and soldering the metal casing to a substrate connected to the device. Unfortunately, this method of shielding is costly and cumbersome because of:
A) High temperatures generated during the soldering process for attaching the metal shield to the device. Heat generated by the soldering process may be conducted directly to the IC and can damage it. Due care is required in order to control the soldering process to prevent jeopardizing the quality of the IC. PA1 B) The additional thickness or bulk required when adding a metal enclosure. The increase in the overall size of the shielded package is substantial, due to the additional thickness of the shield. This results in a package that is larger than optimum. PA1 C) The additional cost associated with the soldering operation. The step of soldering the shield requires additional assembly time and labor, adding further cost to the final package. Providing shielding for integrated circuits in this way requires special mounting and holding fixtures for the shield and the IC package. PA1 Conventional shielded systems also do not provide for dissipation of thermal energy generated by the device. Numerous methods of heat sinking are known in the art, and generally comprise attaching a metal heat sink to the IC package. This approach is not optimal because thermal energy must still travel through the insulating plastic molding compound prior to reaching the metal heat sink. Radio Frequency (RF) power ICs such as amplifiers present special shielding and thermal dissipation problems that are not addressed by the conventional art. PA1 As a result, a need exists for a method to provide RFI shielding and enhanced thermal conductivity to a high-density integrated circuit package that is economical, does not generate excessive temperatures, and provides a low-profile, high-density package.